Re: [Gelato-technical] Serious performance degradation on a RAID with kernel 2.6.11

From: Andreas Hirstius <>
Date: 2005-04-06 17:30:37
Rob Fowler wrote:

> I've recently had discussions with several vendors who have mentioned
> similar magnitudes of disk performance degradation due to the
> coupling of vibration between cooling fans and disks.  This can 
> dramatically increase seek time by keeping the arm from settling.
> In one case, upgrading a chassis fan caused disk throughput to go down
> by a factor of 16.  The solution is careful attention to vibration
> damping in mountings.  Vibration caused by fan bearing wear could have
> a similar effect.
We've also seen similiar problems before... So I made sure it's not 
something "mechanical" ;-)

> Can you go back to your old kernel to verify that it is still
> giving you the same performance?
I'm constantly going back and forth between "working" and "not working" 
The performance with a given kernel doesn't change...


> -- Rob Fowler
> David Mosberger wrote:
>>>>>>> On Tue, 05 Apr 2005 20:11:51 +0200, Andreas Hirstius 
>>>>>>> <> said:
>>   Andreas> Hi, We have a rx4640 with 3x 3Ware 9500 SATA controllers
>>   Andreas> and 24x WD740GD HDD in a software RAID0 configuration
>>   Andreas> (using md).  With kernel 2.6.11 the read performance on the
>>   Andreas> md is reduced by a factor of 20 (!!)  compared to previous
>>   Andreas> kernels.  The write rate to the md doesn't change!! (it
>>   Andreas> actually improves a bit).
>> Is there any reason to believe this change in behavior is
>> ia64-specific?  I doubt it.  The q-syscollect profiles on your
>> web-site shows that the CPU is basically completely idle.  You may
>> want to try 2.6.10 to see whether the bad behavior was introduced
>> before or after that.  Unfortunately, 2.6 is developing very rapidly
>> so you may have to do more binary searching between 2.6.9 and 2.6.10
>> or 2.6.10 and 2.6.11 to pin the problem down to a useful granularity.
>> You may also want to look at the bitkeeper changelogs to see if you
>> can find anything suspicious (you can do that easily via the web by
>> browsing the source code [1]).  Lastly, you may want to ask on
>> linux-kernel whether anybody can think of a change that could have
>> this effect.
>>     --david
>> [1]
>> _______________________________________________
>> Gelato-technical mailing list
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Received on Wed Apr 6 03:32:23 2005

This archive was generated by hypermail 2.1.8 : 2005-08-02 09:20:37 EST